Processing of fish both whole and as a by-product of other operations such as waste from filleting or canning is a large and important business all over the world.
The objective of most waste operations and a large volume of the whole fish processing is to produce an animal or poultry feed in dry form.
The method most generally used is that of the menhaden and related sardine industry. Here the fish are steam cooked and passed directly to a press which produces a solid phase known as press cake which is dried to produce fish meal, and a liquid phase known as raw water, the latter containing considerable quantities of fish oil, which is removed e.g. via a centrifugal pump. The liquor is then concentrated to a syrup of about 50% solids known as fish solubles. The resulting fish solubles is a syrupy, pungent cheesy-odor liquid.
This product is quite valuable as it contains about 70% protein on a dry basis and valuable amino acids, and an unknown growth factor when fed to poultry, hogs or mink.
But it is sticky and too viscous to pump when cold at a concentration much above 50% solids.
Only 40 pounds of the concentrated solubles per ton of broiler mash is required to supply the necessary amino acids and growth factor for commercial broiler feeding. Obviously, it is difficult for the feed manufacturer to blend this small amount of pasty, sticky solubles in liquid form uniformly into a 2,000 lb. batch of dry broiler mash so that a small chick will get the uniform required amount of this valuable material in its daily food.
Many attempts have been made to reduce the solubles to a dry powder, but the dry solubles are so hygroscopic they quickly reabsorb moisture from the air and become sticky and pasty.
Other attempts have been made to dry the concentrated solubles back into the press cake, but the results have not been satisfactory as the solubles form a sticky film on the surface of each particle of pressed fish causing much of the material to stick to the inside shelves of a dryer and burn.
As a result of the above conditions, concentrated fish solubles are a drug on the market, and it is difficult to find a home for all that can be produced even at one-half the price of fish meal. Large quantities of concentrated fish solubles are on hand unsold in the U.S.A., Chile and Peru.